1. Field of the Invention
The invention relates to a touch pad module, more particularly to a touch pad module that includes a touch pad unit separate from a control circuit unit.
2. Description of the Related Art
Various types of touch pads, such as capacitive, resistive, light-sensitive, sound-responsive, etc., are known in the art. Touch pads are usually integrated into electronic devices, such as notebook computers, personal digital assistants, etc. When used in combination with a touch pen, the touch pad can serve as an input device for inputting text. Moreover, with the use of a finger moving on the surface of the touch pad, the touch pad can have the cursor control, item selection and window scrolling functions of a computer mouse.
For a capacitive touch pad, the operating principle thereof is as follows: Finger position is sensed by virtue of the capacitance of the human body. Particularly, at the instant a finger touches the touch pad, a contact capacitance is generated at the surface of the touch pad. Because the surface of the touch pad is formed into a sensing array, and because the touch pad is connected to a control circuit, the control circuit is able to continuously track the finger contact capacitance and to generate position information corresponding to (X, Y) coordinates of the finger contact position. Moreover, since the touch pad is pressure-sensitive, a Z-coordinate of the finger contact position can be determined by the control circuit in accordance with the amount of finger pressure applied to the touch pad.
FIGS. 1 to 3 illustrate a conventional capacitive touch pad module 9 installed in notebook computers. The known touch pad module 9 includes a circuit board 91 and a touch pad unit 92 overlying the circuit board 91. The touch pad unit 92 includes a dielectric layer 921 and a sensing layer 922 disposed between the dielectric layer 921 and the circuit board 91. The circuit board 91 has a first surface adhered to the sensing layer 922 of the touch pad unit 92, and a second surface mounted with a control chip 911 and formed with circuit traces 912. The circuit traces 912 on the circuit board 91 are coupled electrically to the touch pad unit 92 using conductive vias 913. The modular configuration of the touch pad module 9 facilitates mass production and installation on electronic devices.
However, the size of the touch pad module 9 cannot be reduced further in view of physical limitations imposed by the control chip 911 and the circuit traces 912. Moreover, because the touch pad unit 92 is mounted directly on the circuit board 91, which is required to be rigid so as to be able to permit mounting of the control chip 911 and formation of the circuit traces 912 thereon, the conventional touch pad module 9 has a flat configuration and is not suitable for application to curved or rounded surfaces of casings of electronic devices.